Magnetoelastic torque sensor with ambient field rejection

ABSTRACT

The present invention involves a method and apparatus for canceling the effects of magnetic field noise in a torque sensor by placing three sets of magnetic field sensors around a shaft, the first set of field sensors being placed in the central region of the shaft and the second and third sets of field sensors being placed on the right side and left side of the field sensors placed at the central region, respectively. A torque-induced magnetic field is not cancelled with this arrangement of field sensors but a magnetic near field from a near field source is cancelled.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/403,992, filed Mar. 13, 2009, and claims priority under 35U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/036,619,entitled “MAGNETOELASTIC TORQUE SENSOR WITH AMBIENT FIELD REJECTION”,filed Mar. 14, 2008, the entire disclosure of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is related in general to systems and methods involving theuse of magnetic field sensors, and in particular the invention isrelated to systems, methods, and apparatus involving sensors andcircuits that cancel magnetic field noise while measuring torque-inducedmagnetic fields.

2. Description of the Related Art

U.S. Pat. No. 5,351,555, the disclosure of which is incorporated hereinby reference in its entirety, discloses a single circularly magnetizedregion in which the magnetic dipoles tilt in the presence of torsionalstress, thereby emanating an externally measurable magnetic field.Because magnetic fields, in the context of their measurement, arefungible, the sensor taught in the '555 patent may be susceptible toother magnetic fields of exterior origin. In particular, the Earth'smagnetic field will cause a phenomenon known as “compassing,” in whichthe measured field is the sum of the torque dependant field plus theEarth's north-south magnetic field component. Within the context of thisdisclosure, the term “compassing” shall be used to describe any errorresulting from interaction between the magnetic field sensors andmagnetic fields of external origin.

U.S. Pat. No. 5,520,059, the disclosure of which is also incorporatedherein by reference in its entirety, addresses the compassing issue withthe addition of an adjacent second region that is magnetized in theopposite circular direction to the first region. This arrangement yieldstwo torque-dependent magnetic fields and, because the acquiescentmagnetization of the regions is in opposite directions, thetorque-dependent magnetic fields are of equal but opposite magneticpolarity. Corresponding with the two regions described in the '059patent are two magnetic field sensors, each with an opposite axialpolarity to the other (but with the same polarity relative to each ofthe corresponding magnetized regions). Thus, an ambient magnetic farfield affects each of the field sensors in an equal but opposite manner,thereby canceling its measurement. That is, a non-divergent (far) fieldwould affect each of the corresponding field sensors with approximatelyequal magnitude, but with opposite polarity (owing to their installedconfiguration); thus by summing the outputs all common mode externalmagnetic fields would be cancelled.

While the teachings of the '059 patent are effective when dealing withfar fields, a divergent near field can expose each of the two magneticfield sensors to distinctly different field intensities and direction.In this scenario, the two field sensor outputs will not reflect equalbut opposite error components that cancel each other, but rather unequaland opposite components that introduce an error to the measurement. Inpractice, the configuration of the invention disclosed in the '059patent is error-prone in the presence of locally divergent magneticfields because the two magnetic field sensors experience differentmagnitudes of the divergent magnetic fields. The difference in magneticfields between the two magnetic field sensors originating from a nearfield source combines non-uniformly with torque induced magnetic fieldsand leads to a false torque value. Thus, it is important to eliminatethis near field effect.

There are numerous other types of near field sources that can compromisean accurate torque-dependent field measurement. These sources include apermanent magnet, a magnetized wrench, a motor or solenoid, etc. Anotherwould be the nearby presence of a ferromagnetic structure that distortsthe shape and direction of the earth's magnetic field, creating alocalized area in which the magnetic flux is concentrated in anundesirable direction. Each of these examples results in a divergentmagnetic field, i.e., one in which there are significant local gradientsin both magnetic field strength and flux direction.

There are numerous methods for canceling the effects of near fieldsource or stray magnetic fields. These include employing shielding andusing flux directors. Each of these types of structures is made frommaterials having a high magnetic permeability, meaning that they presenta much lower resistance to magnetic fields than, for example, air. Inprinciple, a shield would be in the form of a tube of infinite length,although shorter finite lengths may suitably function. Magnetic fieldsoriginating outside of the shield are effectively shunted through thehighly permeable shield material, which prevents them from intersectingthe field sensors. Using a different approach, a flux director “gathers”most of the torque dependent magnetic field and directs it into themagnetic field sensors. With this approach, the flux director geometryis such that its effectiveness of gathering the torque dependentmagnetic field of interest is much greater than its effectiveness ofgathering extraneous and error inducing magnetic fields, thus increasingthe efficiency of the magnetic field sensors and hence, their signal tonoise ratio.

While the shielding method noted above can be effective for externalmagnetic fields perpendicular to the axial direction of a shield in theform of a tube, this shield is very vulnerable to external magneticfields in the axial direction of the tube which is open at both ends.Any external magnetic fields can transfer to the field sensors insidethe shield through the sides of the shield which are open.

Flux director structures typically operate by gathering the radial fluxcomponent of the torque dependent magnetic field, and are therefore wellsuited for rejecting axially directed flux of external origin, however,flux directors tend to be susceptible to external fields perpendicularto the axis of the shaft.

A combination of tubular shielding and flux directors would act in acomplimentary manner by effectively mitigating both axially and radiallydirected fields of external origin acting directly on the field sensingdevices. However, such a combination has other shortcomings that limitits desirability in many applications including cost and packagingwithin the design.

If an external magnetic field source is directly contacted with the endof a shaft such as the end of the column of an electric power steeringsystem, a strong external near field could transfer to the field sensorsthrough the shaft as a result of diametric variations in the shaft ornearby magnetically coupled structures such as, for example, a bearingor mounting flange. Moreover, a typical manufacturing process for acolumn or shaft may include a magnetic particle inspection (MPI) processthat involves a magnetization process for guiding magnetic particlesinto the defect sites for visualization of defects on column surface,and a demagnetization process after finishing the inspection.Frequently, demagnetization is not perfect, and there remains a remanentmagnetic field in the column or shaft after the MPI process. Typicalvalues of the remanent magnetic fields are between 10 and 100 Gauss.This relatively large external magnetic field can be directlytransferred to the field sensors inside the shield, and can benon-uniformly summed with the torque-induced magnetic fields, corruptingthe torque measurement. This means that there is no totally effectiveway to protect or shield external magnetic fields propagating throughthe shaft with current techniques.

An additional disadvantage of the shielding method is that anydeformation of the shield device caused by mechanical impact or extremetemperature change can affect the relative position of the field sensorsand the shield, which can lead to unbalancing of far field valuesbetween two sensor fields operating in pairs that are oppositelyoriented. This would result in compassing failure.

Furthermore, in most torque sensor applications, packaging space islimited, and in many cases there is no room for a shield or fluxdirector. In addition, the added financial cost for those components isnot insignificant because materials with high permeability tend to havehigh percentages of nickel, the pricing of which is quite volatile.

Based on the foregoing, there is a need for a new and better techniquefor effectively canceling the effects of non-torque dependent magneticfields without using shielding materials or flux directors. The presentinvention meets these requirements by special arrangement of fieldsensors so as to effectively eliminate or minimize measurement errorresulting from divergent near fields without using shielding materialsand flux directing devices.

SUMMARY OF THE INVENTION

The present invention is based on hardware and software for cancellationof external magnetic fields by placing three sets of magnetic fieldsensors above magnetic regions, or regions, conditioned on a shaft. Themagnetic regions on the shaft consists of three sections: (1) centralregion, (2) right side region, and (3) left side region. A first orprimary set of magnetic field sensors is located above the centralregion. A second set of secondary magnetic field sensors is locatedabove the right side region. A third set of secondary magnetic fieldsensors is located above the left side region.

In this scheme, we utilize the fact that, beyond a certain distancebetween the near field source and the sensors, a magnetic field from anexternal near field source(s) decreases in a substantially linearfashion in relation to the distance from the external near field source.Magnetic field sensors placed closest to the external near field sourcesdetect the largest near field value, magnetic field sensors placedfarthest from external near field source detect the smallest near fieldvalue, and magnetic field sensors in the center sense an average valueof the nearest and farthest sets of magnetic field sensors. The magneticfield sensors at the central region have opposite sensing polarity tothe magnetic field sensors at the right side and left side regions.Thus, the near field measured by the primary magnetic field sensors atthe central region is the same magnitude and opposite sign from theaveraged values of the near field measured by the secondary magneticfield sensors at the right and left regions. The interconnects to thefield sensors in combination with the associated electronics areconfigured so as to average the values of the left and right sideregions and sum that average with the value of the center region sensorwhich, because it is oriented with an opposite polarity, effectivelycancels the effects of the near field measurement error.

While the near field is cancelled out, the torque induced magnetic fieldmeasured by these three set of magnetic field sensors is not cancelledout because the output of the center region, or primary sensor, is not acommon mode measurement with respect to the left and right regionsensors.

In addition to the use the three contiguously magnetized regions asdisclosed above, this arrangement of field sensors can be applicable toany number of magnetized regions on the shaft. For example, if thisarrangement is applied to single magnetized region, the magnetic fieldsensors at the central primary region are placed proximate to the centerof the single region. Magnetic field sensors located to the right andleft side of the single magnetized region detect only the near fieldbecause the absence of magnetic polarization proximate to thosesecondary sensors results in the absence of a torque induced magneticfield.

In case of application to a three region magnetized shaft, the magneticfield sensors at the central region and magnetic field sensors at rightside and left side regions measure both near field and torque inducedmagnetic field. The near field is cancelled out and torque inducedmagnetic field is measured.

Accordingly, it is a principal object of the present invention toprovide a torque sensor and method for using the same having amagnetoelastically active region with one or more regionscircumferentially magnetized in order to detect a torque-dependentmagnetic flux emanating from the active region.

It is another object of the present invention to provide a torque sensorand method for using the same in which is provided an arrangement ofmagnetic field sensors proximate to the torque sensor such that thesignal from the sensors measuring the torque-dependent magnetic fluxfrom the active region may be compensated to substantially eliminate theeffects of a near magnetic field source on the torque sensor.

Briefly described, those and other objects and advantages of the presentinvention are accomplished, as embodied and fully described herein, by amethod for reducing the noise in a signal from a torque sensor caused bynear magnetic field sources, the method including the steps of providinga torque sensor, receiving a first primary signal upon the applicationof a torque; receiving a second and a third secondary signals; andadjusting the first signal using the second and third signals therebycompensating for the effects of the near magnetic field source. Thetorque sensor includes at least a longitudinally extending member; amagnetoelastically active region directly or indirectly attached to/orforming a part of the surface of the member, the active region having atleast one region magnetized in a first substantially circumferentialdirection in such a manner that torque applied to the member isproportionally transmitted to the active region; a plurality of primarymagnetic field sensors arranged proximate the at least one region foroutputting a first signal corresponding to a torque-dependent magneticflux emanating from the active region; at least one secondary magneticfield sensor axially spaced in a first direction by a pre-determinedfirst distance from the plurality of active magnetic field sensors foroutputting a second signal corresponding to an ambient magnetic fluxemanating from the near magnetic field source; at least one secondarymagnetic field sensor axially spaced in a second direction opposite thefirst direction by the pre-determined first distance from the pluralityof active magnetic field sensors for outputting a third signalcorresponding to the ambient magnetic flux emanating from the nearmagnetic field source.

DESCRIPTION OF THE SEVERAL DRAWINGS

FIG. 1 is a graph of a magnetic field distribution associated with anAllen wrench measured along the axial direction using a Gauss probe inair;

FIG. 2A is a schematic diagram of a shaft that has beencircumferentially magnetized in opposite directions in two regions andfour field sensors for each region (two of which are not visible);

FIG. 2B is a schematic diagram of the shaft of FIG. 2A showing anexternal magnetic flux due to a torque applied to the shaft;

FIG. 2C is a perspective view schematic diagram of a bobbin around theshaft of FIG. 2A;

FIG. 2D is a perspective cross-sectional view of the bobbin of FIG. 2C;

FIG. 3 is a graph showing a near field effect of the common moderejection scheme measured in air according to one aspect of the presentinvention;

FIG. 4 is a graph comparing a near field effect between the common moderejection method and a new method of the present invention;

FIG. 5 is a graph showing the output response to an axial component of amagnetic field measured along a shaft using a fluxgate sensor;

FIG. 6 is a schematic diagram showing the placement of magnetic fieldsensors around a shaft according to the present invention so as tocancel out near field effects;

FIG. 7 is a perspective view drawing showing a single magnet formagnetization of a shaft to form a single region;

FIG. 8 is a perspective view drawing showing three magnets formagnetization of shaft to form three regions;

FIG. 9 is a graph showing the axial component of magnetic fieldoriginated from a shaft when the shaft is magnetized using a singlemagnet according to FIG. 7;

FIG. 10 is a graph showing the axial component of magnetic fieldoriginated from a shaft when the shaft is magnetized using three magnetsaccording to FIG. 8;

FIG. 11 is a graph showing the mapping of the sensitivity of a shaftmagnetized with three magnets according to FIG. 8;

FIG. 12 is a schematic diagram showing the placement of magnetic fieldsensors around a shaft having a single region according to the presentinvention so as to cancel out near field effects;

FIG. 13 is a schematic diagram showing the placement of magnetic fieldsensors around a shaft having three regions according to the presentinvention so as to cancel out near field effects;

FIG. 14 is a schematic diagram of a shaft having a single region showingthe placement of eight field sensors around the shaft (only six arevisible) to improve rotation signal uniformity compared to using onlyfour field sensors;

FIG. 15 is a schematic diagram of a shaft having three regions showingthe placement of eight field sensors around the shaft (only six arevisible) to improve rotation signal uniformity compared to using onlyfour field sensors;

FIG. 16 is schematic diagram of a shaft having three regions showing theplacement of field sensors with 45 degrees between field sensors in thecircumferential direction;

FIG. 17 is a schematic diagram of a shaft having three regions showingan alternative placement of field sensors with 45 degrees between fieldsensors in the circumferential direction;

FIG. 18 is a perspective drawing of a shaft having two regions showingthe placement of field sensors around the shaft; and

FIG. 19 is a graph showing the magnetic field mapping of the shaft ofFIG. 18.

DETAILED DESCRIPTION OF THE INVENTION

Several preferred embodiments of the invention are described forillustrative purposes, it being understood that the invention may beembodied in other forms not specifically shown in the drawings. Thefigures will be described with respect to the system structure andmethods for using the system to achieve one or more of the objects ofthe invention and/or receive the benefits derived from the advantages ofthe invention as set forth above.

U.S. Pat. No. 5,520,059 describes a torque sensor having a transducerand magnetic field vector sensor. The torque sensor is mounted on ashaft which is part of a machine, and it rotates about a centrallongitudinal axis. A torque having a magnitude T is applied at oneportion of the shaft and is transmitted thereby to another portion ofthe shaft where the motion of the shaft due to the torque T performssome useful work. The torque may be in a clockwise or counterclockwisedirection when looking at the visible end of the shaft, but obviously itcan be applied to rotate the shaft in either or both directionsdepending on the nature of the machine incorporating the shaft.

The transducer is firmly attached to or integral to the shaft in one ofa number of ways, and acts as a means for providing a magnetoelasticallyactive region on the shaft. In practice, the transducer will generallytake the form of a cylindrical sleeve or ring with end faces, an innersurface, and an outer surface, suitably attached to the shaft at aconvenient location along the axis which is within the torsionallystressed region of the shaft, it may be an integral and homogeneous partof the shaft, or it may be an integral and homogeneous part of the shaftdistinguished by having a different metallurgical phase than the rest ofthe shaft as disclosed in U.S. Pat. No. 6,047,605. The transducer isendowed, by prior processing or, in the case of a ring or collar, as acollateral effect to the means of attachment to the shaft, with aneffective uniaxial magnetic anisotropy having the circumferentialdirection as the easy axis. In addition, the transducer will also bemagnetically polarized in one or the other circumferential direction byany effective method, several of which are described in the '059 patent.Briefly, the active region of the transducer is magnetically polarizedin a substantially purely circumferential direction, at least to theextent that, in the absence of the torque T (in a quiescent state), ithas no net magnetization component in the direction of the axis and hasno net radial magnetization components. Thus, the domains whosemagnetizations originally had components in the opposite circular senseare substantially reversed such that all of the domains are of the samepolarity. If the circular anisotropy is suitably dominant, all of thedomain magnetizations will lie within at most a plus or minus 45 degreelimit of the circumferential direction, and will be symmetricallydistributed within small enough volumes of the ring or portion of theshaft to ensure that no uncompensated external flux is sensible by themagnetic field vector sensor. The closed cylindrical shape of thetransducer enhances the stability of the polarization of the transducerby providing a complete magnetic circuit.

Due to the construction and processing of the transducer, specificallythe magnetoelastic properties of the active region, the application oftorsional stress to the shaft and thus to the active region of thetransducer causes reorientation of the polarized magnetization in thetransducer such that the magnetic domains align with principal stressaxes. The polarized magnetization becomes increasingly helical as thetorsional stress increases owing to the fact that torsional stressresults in a helically aligned stress axis. The helicity of themagnetization in the transducer depends on the magnitude of thetransmitted torque T, and the chirality is dependent on thedirectionality of the transmitted torque and the magneto elasticcharacteristics of the transducer. The helical magnetization resultingfrom the torsion of the transducer has both an internal circumferentialcomponent in one direction an external axial component and an externalradial component. As described below in more detail, the axial andradial components are within the same flux path, that is to say that thehelicity of the magnetization results in magnetic flux existing at oneboundary of the active region, traveling in space externally along thelongitudinal axis of the shaft, and reentering the shaft at the oppositeboundary of the active region. Of particular importance is that themagnitudes of both the radial and axial components depends entirely onthe torsion in the transducer while the flux direction, or polarity, ofboth the radial and axial components are dependent upon the direction inwhich the torque is applied to the shaft.

The magnetic field vector sensor is a magnetic field vector sensingdevice located and oriented relative to the transducer so as to sensethe magnitude and polarity of the axial and/or radial field componentsarising in the space about the transducer as a result of thereorientation of the polarized magnetization from the quiescentcircumferential direction to a more or less steep helical direction. Themagnetic field vector sensor provides a signal output reflecting themagnitude of the torque T. The magnetic field vector sensor preferablycomprises one or more solid state sensing devices, such as Hall effect,magnetoresistance, magnetotransistor (“magnistor”), magnetodiode, orMAGFET (Magnetic Field Effect Transistor) field sensors. Other possiblefield sensors include non-linear cores, having magnetic propertiesvarying with H (defined as a magnetizing force), magnetometers, and fluxgate magnetometers, and coils (either encircling or proximate,intercepting flux and having an induced EMF proportional to dΦ/dt, orchange in magnetic flux over change in time). One or more wires connectthe magnetic field vector sensor to a source of direct or alternatingcurrent power or excitation signal, and transmit the signal output ofthe magnetic field vector sensor to a receiving device, such as acontrol or monitoring circuit for the machine or system incorporatingthe shaft.

The '059 patent addresses the compassing issue seen with previous torquesensors by adding one or more magnetoelastically active regions(hereinafter simply referred to as a “region”) adjacent the firstregion, which are also magnetized in the opposite circular direction tothe first region that is used for torque-sensing purposes. Two sets ofmagnetic field sensors are placed on the first and second magneticregion. The magnetic field sensors in each set have opposite axialpolarity to the other. Thus, a uniform magnetic field is cancelled dueto this opposite arrangement of magnetic field sensors. When anon-uniform magnetic field is applied to the sensor system, the two setsof magnetic field sensors would see different values of the magneticfield.

Turning to FIG. 1, shown therein is a graph 100 of a magnetic fielddistribution 102 for an Allen wrench measured along the axial directionof the wrench using a Gauss probe in air as it is moved away from thewrench. As shown in FIG. 1, the magnetic field at the surface of theAllen wrench tail was 30 Gauss, and decreased as the distance increasedfrom the tail. Thus, the Allen wrench emanates a non-uniform magneticfield source that decreases non-linearly until it reaches an asymptote,at which point it becomes substantially linear. If the end of the Allenwrench is brought close, for example, less than 1 cm, to the sensorsystem of the '059 patent, then the difference in the magnetic fieldseen by the two different sets of field sensors could easily be morethat 20 Gauss. Magnetic field sources such as permanent magnets,solenoids, and magnetized ferromagnetic materials would show a similarmagnetic field profile in air and have similar effects on the twodifferent sets of field sensors.

Turning now to FIG. 2A, shown therein is a schematic diagram of a shaft202 that has been circumferentially magnetized in opposite directions,as shown by the arrows A, B, in two regions, 204, 206, respectively. Theshaft 202 may be solid or hollow, and it is preferably homogeneous, atleast in the region of the two regions 204, 206. Each of the regions204, 206, includes four field sensors arranged approximately equaldistance from each other around and above the surface of the shaft 202.That is, field sensors L1, L2, L3, and L4 (not visible) are arrangedaround the region 204, and field sensors R1, R2, R3, and R4 (notvisible) are arranged around the region 206. Each sensor may be arrangedas shown by the respective arrows l1, l2, l3, l4, r1, r2, r3, r4, todetect the polarity of magnetic field emanating from the shaft 202corresponding to the arrow directions.

FIG. 2A represents a sensor system disclosed in U.S. Pat. No. 5,520,059.The two magnetic regions 204, 206, having opposite circular directionsare encoded on the shaft. There are four field sensors associated witheach region to average out the undesirable rotational non-uniform fieldobserved as the shaft 202 rotates that can result from inhomogeneity ofthe material composition or metallurgical phase and other factors. Themagnetic field sensors on each magnetic region have opposite axialpolarity to the other so that a uniform magnetic field along the axialdirection can be cancelled out. A far magnetic field such as the Earth'smagnetic field, can be cancelled out easily by pairing field sensorswith opposite orientation to create a common mode rejection scheme asproposed in U.S. Pat. No. 5,520,059. However, as noted previously, thatarrangement cannot easily eliminate near fields due to the non-uniformand short-range character of the magnetic near field as shown in FIG. 1.

FIG. 2B is a schematic diagram of the shaft 202 of FIG. 2A showing anexternal magnetic flux caused by a torsional load applied to the shaft202, where the external magnetic flux can be described in terms of aradial component 208 and an axial component 210. FIG. 2C is aperspective view schematic diagram of a bobbin 212 around the shaft 202,which is used for, among other things, to hold the field sensors R1, R3,L1, and L2 in a fixed position above the surface of the shaft 202 (asbest seen in FIG. 2D).

Turning now to FIG. 3, shown therein is a graph 300 depicting a nearfield effect of the common mode rejection scheme illustrated in FIG. 2Ameasured with the sensors mounted in a bobbin 212 and with no shaftpresent. The Y axis values represent the voltage output of the sensorinterface electronics which is, in turn, representative of the measuredmagnetic field strength. A near field source was moved toward the rightside, and aligned with the axis of the bobbin 212, producing a nearfield effect. In the graph 300, the aforementioned magnetized Allenwrench was used to simulate the near field effect. The line 302 (solidsquare symbols) represent a magnetic near field signal picked up by themagnetic field sensors R1, R2, R3, and R4. The line 304 (solid trianglesymbols) represent magnetic near field signal picked up by the magneticfield sensors L1, L2, L3, and L4. The line 306 (solid circle symbols) isthe difference between the values on line 302 and line 304. The line 306shows that the common mode rejection scheme cannot reject a near fieldsource located close to the field sensors.

As shown in the graph 300, the signal seen by the field sensors R1, R2,R3, and R4 is stronger than the signal seen by the field sensors L1, L2,L3, and L4 because the near field source (Allen wrench) is located inthe right side of the bobbin 212, so it is closer to the field sensorsR1, R2, R3 and R4. The opposite sign between the line 302 and the line304 is due to the opposite axial polarity of the field sensors R1, R2,R3, and R4, and the field sensors L1, L2, L3, and L4. If the right andleft field sensors see the same magnitude of the near field, theaddition of the signals from the two sets of field sensors should bezero, which would eliminate the near field effect. However, that is notthe case, as shown by line 306, which shows the resultant imbalance ofright side versus left side sensor outputs.

Turning now to FIG. 4, shown therein is a graph 400 comparing the nearfield effect between the common mode rejection method currently used,the near field effect of the common mode rejection method currently usedbut with the addition of a tubular shaped shield surrounding andcomprising the outer surface of the bobbin 212, and the method accordingto the present invention. In each case, only a bobbin 212 holding asensor array was used for illustrative purposes, i.e., there was noshaft present. The Y axis values represent the voltage output of thesensor interface electronics which is, in turn, representative of themeasured magnetic field strength. A near field source was moved towardthe right side, and aligned with the axis of the bobbin 212. In thegraph 400, the line 402 (solid square symbols) represents the prior artcommon mode rejection method without a shield. The line 404 (solidtriangle symbols) represents the prior art common mode rejection methodwith a cylindrical open tube shield fabricated from Fe—Si highpermeability material. The line 406 (solid circle symbols) representsthe common mode rejection method according to the present invention. Asshown in the graph 400, using a shield improves the cancellation effectof a near field, but a large amount of the interfering magnetic field isstill seen, especially when the near field source is close to the bobbin212 containing the sensor array. As shown by line 406, a statisticallysignificant improvement in the cancellation of the near field effect wasachieved with the method of the present invention.

Turning back to FIG. 1, the magnetic field of the near sourcerepresented by the line 102 can be considered to decrease linearlypiecewise. The measurement in FIG. 1 was performed using a Gauss probe.No high permeability materials were located around the wrench and theGauss probe. When a magnetic field source is contacted with the end of acylindrical shaft made of soft magnetic material, the magnetic field onthe surface of the shaft shows a wide ranging linear decrease in themagnetic field from the contact point of the magnetic field source asshown in FIG. 5, which is a graph 500 of the output response to an axialcomponent of a magnetic field measured along a shaft using a fluxgatesensor. In this case, the magnetized Allen wrench of FIG. 1 contacts theend of the shaft. The magnetic field was measured using a fluxgatesensor coil. The long axis of the sensor coil, which is the axis ofmaximum sensitivity, was parallel to the cylindrical axis of the shaftand the coil was offset about 1 mm from the surface of the shaft. Thereference position of the scan and the output voltage from the fluxgatesensor coil at the reference positions were set to (0,0). The distancebetween the reference position and the end position of the scan was 2.5cm. Thus, the starting point for line 502 at distance 0 is away from thenear field source and approaches the near field source at distance 2.5.As the fluxgate sensor moves closer to the near field source, the signalincreases linearly. This linear behavior shown in line 502 is due to thehigh permeability material that confines the diverging magnetic fieldsin the shaft 202.

Turning now to FIG. 6, shown therein is a schematic diagram in whichprimary magnetic field sensors C1 and C2 and secondary field sensors Rand L are shown arranged around a shaft 602 according to the presentinvention, such that they cancel out near field effects from a nearfield source 604. The two primary field sensors C1 and C2 are arrangedabove the surface of the shaft 602 approximately near the center of theshaft 602 relative to the two ends of the shaft 602. One secondarysensor coil R is arranged above the surface of the shaft 602 closer tothe right side of the shaft 602. One secondary sensor coil L is arrangedabove the surface of the shaft 602 closer to the left side of the shaft602.

The near field source 604 is located, as shown, on the right side of theshaft 602. It may be in contact with the end of the shaft 602.

The shaft 602 is not magnetically conditioned. Therefore, the magneticfield sensors C1, C2, R, and L would only see the magnetic near fieldcreated by the near field source 604. The profile of the magnitude ofthe magnetic field along the longitudinal direction of the shaft willlook like the dotted line 606, and increase linearly from left to right,as also shown in FIG. 5.

Table 1 shows a calculation of the near field effect seen by the foursensors C1, C2, R, and L due to the magnetic field from the near fieldsource 604. The magnitude of the near field seen by the sensor R islarger than the magnitude seen by all the field sensors because it isphysically closest to the near field source 604. The magnitude of thenear field seen by the sensor L is smaller than the magnitude seen byall the field sensors because it is physically farthest from the nearfield source 604. If the distances between the field sensors R and C1 orC2 and the distances between the field sensors L and C1 or C2 are thesame, then one can tabulate the near field distribution as shown inTable 1. In the example of Table 1, the maximum measurement value isnormalized to 3 generic units for illustrative purposes. The actualcomputation of the net near field effect value shown in Table 1 could beperformed by an arithmetic logic unit (ALU) 608.

TABLE 1 Near field effect calculation. Near field Net near Near fieldvalue seen field Position value by coil effect C1 2 2 0 C2 2 2 R 3 −3 L1 −1

Turning now to FIGS. 7 and 8, shown therein are perspective viewdrawings showing, in one case, a single magnet 704 used to remanentlymagnetize or condition a shaft 702 to form a single region 706 having acircumferential magnetization, and in the other case, three magnets 804a, 804 b, and 804 c used to remanently magnetize or condition a shaft802 to form three regions 806, 808, 810. The direction of magnetizationof the center magnet 804 b is opposite to the other two magnets 804 aand 804 c. Thus, the direction of the circumferential magnetization inthe central region 808 is opposite the circumferential magnetization inthe regions 806 and 810, as indicated by the direction of the arrows.

FIG. 9 is a graph 900 showing the axial component of the magnetic fieldoriginating from the shaft 702 when the shaft 702 is magnetized usingthe single magnet 704 according to FIG. 7 and some nominal amount oftorque is applied to the shaft in order to generate a torque dependentmagnetic field. FIG. 10 is a graph 1000 showing the axial component ofthe magnetic field originating from the shaft 802 when the shaft 802 ismagnetized using the three magnets 804 a, 804 b, 804 c according to FIG.8 and some nominal amount of torque is applied to the shaft in order togenerate a torque dependent magnetic field. As can be seen in FIGS. 9and 10, the magnetic profiles of the axial components of the magneticfield emanating from shafts 702 and 802 are symmetrical in shape.

Turning now to FIG. 11, shown therein is a graph 1102 of a mapping ofthe sensitivity of the shaft 802 after it has been magnetized with thethree magnets 804 a, 804 b, 804 c, according to FIG. 8, in which atorque T is applied to the shaft 802. The center of the line 1102 showsa positive level of sensitivity, which corresponds to thetorque-dependent field arising from the center region 808. The twonegative levels of sensitivity corresponding to the right and leftregions 806, 810 which were circumferentially magnetized in oppositepolarity to that of the center region 808.

Magnetic field sensors were arranged around the shaft 802 at a positioncorresponding to the peak positive level of sensitivity as shown in thegraph 1102 so that maximum torque-induced magnetic field would be seen.If, in an application of the present invention there are spacelimitations or geometry concerns, one or more field sensors to the rightand left may be positioned a distance from the peak positive level ofsensitivity with some loss of sensor sensitivity without departing fromthe nature and scope of the present invention.

FIG. 12 is a schematic diagram showing the placement of magnetic fieldsensors C1, C2, R, and L around a shaft 1202 having a single region 1206according to the present invention, which is an arrangement forcanceling out the magnetic near field effects from the near field source1204. The shaft 1202 is magnetically conditioned with a single magnet(not shown), thereby forming the region 1206 having a remanentcircumferential magnetization in the shaft 1202.

The primary magnetic field sensors C1, C2 near the center of the shaft1202 measure the torque-induced magnetic field from the region 1206 andthe magnetic near field from the near field source 1204. The secondarymagnetic field sensors R, L at the right and left side of the shaft1202, respectively, measure only the magnetic near field because nomagnetic regions exist on the regions of the shaft 1202 where thosefield sensors are arranged. Table 2 shows a calculation of thetorque-induced magnetic field and the magnetic near field effect seen bythe four field sensors C1, C2, R, and L in FIG. 12, which may beimplemented by use of appropriate arithmetic logic unit circuits and/orsoftware element(s) that are well known to those skilled in the art. Theunwanted magnetic near field is cancelled out, and only thetorque-induced magnetic field sensed by the primary field sensors C1, C2near the region 1206 remains. In the example of Table 2, the maximummeasurement value is normalized to 3 generic units for illustrativepurposes. The actual computation of the net near field effect value andthe net torque-induced field value shown in Table 2 could be performedby an arithmetic logic unit (ALU) (as shown in FIG. 6, for example).

TABLE 2 Magnetic field effect calculation for three regions Torque-induced Net Torque- field Net Near field near induced value torque- Nearfield value seen field field seen by induced Position value by coileffect value coil field value C1 2 2 0 T T 2T C2 2 2 T T R 3 −3 0 0 L 1−1 0 0

FIG. 13 is a schematic diagram showing the placement of primary magneticfield sensors C1 and C2 and secondary magnetic field sensors R and Laround a shaft 1302 having three magnetized regions 1306, 1308, 1310,according to the present invention, which is an arrangement forcancelling out the magnetic near field effects from the near fieldsource 1304. The shaft 1302 is magnetically conditioned using threemagnets (not shown), thereby forming the regions 1306, 1308, 1310,having remanent circumferential magnetizations in the shaft 1302.

The primary magnetic field sensors C1 and C2 measure the torque-inducedmagnetic field and the magnetic near field emanating from the centerregion. The secondary field sensors R and L, at the right and left sideof the shaft 1302 measure the torque-induced magnetic fields emanatingfrom the right and left sides of the shaft, respectively, as well as themagnetic near fields at those locations. While the magnetic near fieldmeasured by the secondary field sensors R and L is canceled out by themagnetic near field as measured by the primary field sensors C1 and C2(because they are oppositely oriented), the torque-induced magneticfields seen by field sensors C1 and C2 are not canceled out by thevalues measured by the secondary field sensors R and L. Actually, thetorque-induced magnetic fields are additive due to the oppositelypolarized magnetization between the center region 1308 and the regions1306 and 1310. Table 3 shows a calculation of the torque-inducedmagnetic field and the magnetic near field effect seen by the four fieldsensors C1, C2, R, and L in FIG. 13, which may be implemented by use ofappropriate arithmetic logic circuits and/or software elements that arewell known to those skilled in the art. The unwanted magnetic near fieldis cancelled out, and only the torque-induced magnetic field is seen bythe primary field sensors C1, C2 at the center region 1308. Thetorque-induced magnetic fields emanating from side regions 1306 and 1310are doubled by adding the values from the secondary field sensors R andL. In the example of Table 3, the maximum measurement value isnormalized to 3 generic units for illustrative purposes. The actualcomputation of the net near field effect value and the nettorque-induced field value shown in Table 3 could be performed by anarithmetic logic unit (ALU) (as shown in FIG. 6, for example).

TABLE 3 Magnetic field effect calculation for three regions Torque-induced Net Torque- field Net Near field near induced value torque- Nearfield value seen field field seen by induced Position value by coileffect value coil field value C1 2 2 0   T T 4T C2 2 2   T T R 3 −3 −T TL 1 −1 −T T

FIG. 14 is a schematic diagram of a shaft 1402 having a single region1404 showing the placement of eight field sensors around the shaft 1402(only six are visible) to improve the rotational signal uniformity ofthe magnetic fields seen by the field sensors compared to using onlyfour field sensors. Primary magnetic field sensors C1, C2, C3, C4 (notvisible) are arranged approximately equidistant from each other aroundand above the surface of the shaft and approximately in the center ofthe region 1404. The pair of secondary field sensors R1, R2 and the pairof secondary field sensors L1, L2 (not visible) are spaced approximatelythe same distance from the field sensors C1, C2, C3, C4 in alongitudinal direction of the shaft 1402.

Similarly, FIG. 15 is a schematic diagram of a shaft 1502 having threeregions 1504, 1506, 1508 showing the placement of four primary fieldsensors C1, C2, C3, C4 (not visible) around the center region 1506, twosecondary field sensors R1, R2 around the right region 1508, and twosecondary field sensors L1, L2 (not visible) around the left region 1504of the shaft 1502 to improve the rotational signal uniformity of themagnetic field seen by the field sensors compared to using only fourfield sensors.

FIG. 16 is schematic diagram of a shaft 1602 having three regions 1604,1606, 1608 showing the placement of field sensors with 45 degreesbetween the field sensors 1610, 1612, 1614, 1616 in the circumferentialdirection. FIG. 17 is a schematic diagram of the shaft 1602 having thethree regions 1604, 1606, 1608 showing an alternative placement of thefield sensors 1610, 1612, 1614, 1616 with 45 degrees between fieldsensors in the circumferential direction. The field sensors 1610, 1612,1614, 1616 are closely located along the circumferential direction sothat the field sensors can avoid the magnetic near field at the opposite(rear) side of shaft (near source is not visible). This scheme alsocould enhance the rotational signal uniformity if the shaft 1602 needsto rotate a finite angle, not a full rotation. The field sensors 1610,1612, 1614, 1616 can be placed only near a part of the shaft 1602 havinga uniform field, and would not see the rotational signal from the partof the shaft 1602 having a non-uniform field. Such an embodiment mightbe desired if the shaft is not circumferentially symmetric such as wouldbe the case if a flat or keyway section is present.

Because the torque-dependent fields emanating from each region have botha radial component and an axial component, other embodiments of thepresent invention could also be realized by the use of field sensorsarranged and positioned to detect the radial components of the torquedependent field as well as the radially-directed magnetic fields ofexternal origin.

Of course, the closer the near field interference source is to thesensing regions, the more non-linear the magnitude of the interferingfield will be over the axial extent of the sensor locations, which mayreduce the effectiveness of the field sensors in providing for thecancellation of noise due to near field sources.

In contrast, because the regions embodied in the '059 patent areimmediately proximate, they more closely reflect that of a single pointmeasurement, which is highly susceptible to error in the presence of ahighly divergent “noise” field. Related to this is the fact that, if theinterfering field originates at either end of the shaft, it willpredominately affect the nearest of the two sensing regions, againcausing an error inducing measurement bias. The size of magnetic regionscan be varied for different applications. The number of field sensorscan also be varied depending on different applications.

The present invention cancels out the near field effect more effectivelythan the prior art dual region, dual sensor array common mode rejectionscheme as taught in the '059 patent, especially for near fieldstransferring through the axial direction of the shaft because the fieldsensors placed near each of the oppositely magnetized regions experiencedifferent magnitudes of the near field. The field sensor coils locatedcloser to the near field source sense a higher magnitude of the nearfield than the field sensors located away from the near field source. Atypical separation between the paired field sensors in the common moderejection scheme is about 2 cm. As can be seen from FIG. 5, thedifference in signal between two points 2 cm apart is very large, enoughto significantly affect the true torque value being measured. Even usinga shield device in a cylindrical tube shape surrounding the torquesensing shaft cannot attenuate near field transfer through the axialdirection of the shaft.

The present invention, therefore, eliminates the effect of a strong nearfield transferring through the shaft by arrangement of the field sensorsalong the shaft so as to cancel out the near field signals. The primaryfield sensors at the center of the shaft or region are oppositelyoriented with respect to the secondary field sensors on either side ofthe center field sensors. The distances from the right sensor coil andcenter sensor coil, and from the left sensor coil and center sensorcoil, are preferably the same or approximately the same. A lineardecrease of the near field along the axial direction of the shaft fromthe near field source results in the sensor array cancelling out thenear field effect, as can be seen in Tables 1, 2 and 3.

Thus, an advantage of the present invention over the device of the '059patent is its effective capability of handling various near fieldsources. In the '059 patent, there is no function to eliminate the nearfield effect such as near field transferring though a shaft, which is incontact to the near field source or located close to the near fieldsource even with it being protected by a shielding device. One fieldsensor of the pair located closer to the near field source sees a largermagnetic near field level than the other field sensor, thus anunbalanced signal output between the paired field sensors is produced,significantly altering the true torque-induced signal.

An alternate embodiment of the present invention eliminates not only anear field scenario in which the magnitude decreases linearly from thenear field source, but also the near field scenario in which themagnitude decreases nonlinearly from the near field source. The latternear field scenario can happen when the active regions of a shaft andcorresponding sensor array is in close proximity to a ferromagneticstructure such as a flange, a bearing, or even a shaft section having alarger diameter, (ferromagnetic asymmetry) and either the right fieldsensors or the left field sensors are in the proximity of thisferromagnetic asymmetry. In this situation the interfering fieldmanifests as a nonlinearly varying near field effect due to the closepresence of a ferromagnetic asymmetry, which increases the near fieldeffect to the field sensor located close to the asymmetric ferromagneticstructure.

In order to compensate for the nonlinear property of this type ofinterfering field, the right and left secondary sensors are located witha corresponding asymmetry of distances from the center primarysensor(s). For example, without the presence of a ferromagneticasymmetry or the ferromagnetic asymmetry being located far enough awayfrom field sensors for the interfering field to be substantially linearas shown in the curve of FIG. 1, the distance between the centersensor(s), and the respective right and left sensors are the same. Butin this alternate embodiment where a ferromagnetic asymmetry is locatedin proximity to either the right or left sensor(s), the distance betweenthe sensor located closest to the ferromagnetic asymmetry and the centersensor is reduced by some amount relative to the distance between thecenter primary sensor and the secondary sensor(s) located farthest fromthe ferromagnetic asymmetry. By biasing the distance of one outboardsecondary sensor array from the center primary sensor array in relationto the other outboard secondary sensor array, their average outputvalues are, in effect, weighted in such a manner as to provide areasonable approximation of the magnitude of the interfering field seenby the center sensor(s). The optimal positions of the right sensor(s)and left sensor(s) can be determined by measuring and mapping the actualinterfering field along the axial direction of a shaft and/or simulationvia computer modeling to determine what the necessary biasing distancesbetween the outboard and center sensors must be in order to provide aweighted average field measurement that yields an accurate approximationof what the interfering field strength is at the center sensor arraylocation.

In each of the previous embodiments of the present invention, thesensors have been oriented in such a manner as to measure the axialcomponent of the torque-dependent magnetic field. In other embodimentsof the present invention, as depicted in FIG. 18, the axes of thesecondary sensors R1 and R2, primary sensors C1, C2, C3, and C4 (notvisible), and secondary sensors L1 and L2 (also not visible) can beoriented normal to the surface of the shaft 1802 such that they measurethe radial component of the torque-dependent field which, owing to theshape of the flux path between the poles of the active region, ismanifested by a higher magnetic flux density. Such an embodiment mightbe more suitable if, for example higher sensitivity is required, or themagnetic conditioned region is narrow in relation to the length of theindividual magnetic field sensors. The radial magnetic field componentmeasurement can be performed either by using the dual regionmagnetically conditioned region as taught in the prior art'059 patentwith placement of coils in the middle of each of the oppositelypolarized magnetic regions of the active region and at the boundary 1804between the two oppositely polarized regions as shown in FIG. 18 FIG. 19is a graph showing the magnetic field mapping of the shaft 1802 of FIG.18, showing the axial and radial components of the magnetic field.

Although certain presently preferred embodiments of the disclosedinvention have been specifically described herein, it will be apparentto those skilled in the art to which the invention pertains thatvariations and modifications of the various embodiments shown anddescribed herein may be made without departing from the spirit and scopeof the invention. Accordingly, it is intended that the invention belimited only to the extent required by the appended claims and theapplicable rules of law.

I claim:
 1. A method for reducing the noise in a signal from a torquesensor caused by near magnetic field sources, the method comprising thesteps of: providing a torque sensor comprising: a longitudinallyextending member; a magnetoelastically active region directly orindirectly attached to or forming a part of the surface of the member insuch a manner that torque applied to the member is proportionallytransmitted to the active region, the active region comprising at leastone region magnetically polarized such that the magnetized polaritybecomes increasingly helically shaped as the applied torque increases;at least one primary magnetic field sensor arranged proximate the atleast one region for outputting a first signal corresponding to atorque-dependent magnetic flux emanating from the active region; atleast one secondary magnetic field sensor axially spaced in a firstdirection by a pre-determined first distance from the at least oneprimary magnetic field sensor for outputting a second signalcorresponding to an ambient magnetic flux emanating from a near magneticfield source; at least one secondary magnetic field sensor axiallyspaced in a second direction opposite the first direction apre-determined second distance from the at least one primary magneticfield sensor for outputting a third signal corresponding to the ambientmagnetic flux emanating from the near magnetic field source; receivingthe first signal upon application of the torque; receiving the secondand third signals; and adjusting the first signal using the second andthird signals thereby compensating for effects of the near magneticfield source.
 2. The method of claim 1, wherein the at least one regionis magnetized so that all of the domain magnetizations in the region liewithin at most a plus or minus 45 degree limit of a circumferentialdirection of the member.
 3. The method of claim 1, wherein the magneticfield sensors are vector sensors.
 4. The method of claim 3, wherein thevector sensors are one of a Hall effect, magnetoresistance,magnetotransistor, magnetodiode, MAGFET field sensors, or fluxgatemagnetometer.
 5. The method of claim 1, wherein the member is a shaftincorporated in an on-road or off-road vehicle, a ship, or an industrialprocess.
 6. The method of claim 1, wherein the pre-determined first andsecond distances are substantially the same.
 7. The method of claim 1,wherein the pre-determined first and second distances are such that anaverage of the second and third signals approximates the value of theambient magnetic flux present at the location of the at least oneprimary magnetic field sensor.
 8. The method of claim 1, wherein thetorque sensor comprises two primary magnetic field sensors; onesecondary magnetic field sensor axially spaced in the first direction;and one secondary magnetic field sensor axially spaced in the second,opposite direction.
 9. The method of claim 8, wherein one of the primarymagnetic field sensors and one of the secondary magnetic field sensorsare arranged on one side of the member, and wherein the other of theprimary magnetic field sensors and the other of the secondary magneticfield sensors are arranged on an opposite side of the member.
 10. Themethod of claim 8, wherein all four of the field sensors are arrangedsubstantially on one side of the member and approximately opposite thenear magnetic field source on the opposite side of the member.
 11. Themethod of claim 1, wherein the torque sensor comprises four primarymagnetic field sensors; two secondary magnetic field sensors axiallyspaced in the first direction; and two secondary magnetic field sensorsaxially spaced in the second, opposite direction.
 12. The method ofclaim 1, wherein the active region comprises two axially-spaced regions,the first being magnetized in a first substantially circumferentialdirection and the other being magnetized in a second substantiallycircumferential direction opposite the first direction in such a mannerthat the torque applied to the member is proportionally transmitted tothe active region, wherein the at least one secondary magnetic fieldsensor axially spaced in the first direction is proximate one of theregions, and wherein the at least one secondary magnetic field sensoraxially spaced in the second, opposite direction is proximate the otherregion.
 13. The method of claim 12, wherein the torque sensor comprisestwo primary magnetic field sensors; one secondary magnetic field sensoraxially spaced in the first direction; and one secondary magnetic fieldsensor axially spaced in the second, opposite direction.
 14. The methodof claim 13, wherein one of the primary magnetic field sensors and oneof the secondary magnetic field sensors are arranged on one side of themember, and wherein the other of the primary magnetic field sensors andthe other of the secondary magnetic field sensors are arranged on anopposite side of the member.
 15. The method of claim 12, wherein thetorque sensor comprises four primary magnetic field sensors; twosecondary magnetic field sensors axially spaced in the first direction;and two secondary magnetic field sensors axially spaced in the second,opposite direction.
 16. The method of claim 12, wherein the primary andsecondary magnetic field sensors are oriented substantially normally tothe surface of the member.
 17. The method of claim 1, wherein the activeregion comprises three axially-spaced regions, the middle region beingmagnetized in a first substantially circumferential direction and theouter regions being magnetized in a second substantially circumferentialdirection opposite the first direction in such a manner that the torqueapplied to the member is proportionally transmitted to the activeregion, wherein the at least one secondary magnetic field sensor axiallyspaced in the first direction is proximate one of the outer regions, andwherein the at least one secondary magnetic field sensor axially spacedin the second, opposite direction is proximate the other outer region.18. The method of claim 17, wherein the torque sensor comprises twoprimary magnetic field sensors; one secondary magnetic field sensoraxially spaced in the first direction; and one secondary magnetic fieldsensor axially spaced in the second, opposite direction.
 19. The methodof claim 18, wherein one of the primary magnetic field sensors and oneof the secondary magnetic field sensors are arranged on one side of themember, and wherein the other of the primary magnetic field sensors andthe other of the secondary magnetic field sensors are arranged on anopposite side of the member.
 20. The method of claim 17, wherein thetorque sensor comprises four primary magnetic field sensors; twosecondary magnetic field sensors axially spaced in the first direction;and two secondary magnetic field sensors axially spaced in the second,opposite direction.
 21. The method of claim 20, wherein all four of thefield sensors are substantially on one side of the member andapproximately opposite the near field source on the opposite side of themember.
 22. The method of claim 17, wherein the primary and secondarymagnetic field sensors are oriented substantially normally to thesurface of the member.
 23. The method of claim 22, wherein the primaryand secondary magnetic field sensors are oriented substantially normallyto the surface of the member at the respective boundaries between theregions.
 24. A torque sensor comprising: a longitudinally extendingmember; a magnetoelastically active region directly or indirectlyattached to or forming a part of the surface of the member in such amanner that torque applied to the member is proportionally transmittedto the active region, the active region comprising at least one regionmagnetically polarized such that the magnetized polarity becomesincreasingly helically shaped as the applied torque increases; at leastone primary magnetic field sensor arranged proximate the at least oneregion for outputting a first signal corresponding to a torque-dependentmagnetic flux emanating from the active region; at least one secondarymagnetic field sensor axially spaced in a first direction by apre-determined first distance from the at least one primary magneticfield sensor for outputting a second signal corresponding to an ambientmagnetic flux emanating from a near magnetic field source; at least onesecondary magnetic field sensor axially spaced in a second directionopposite the first direction by a pre-determined second distance fromthe plurality of primary magnetic field sensors for outputting a thirdsignal corresponding to the ambient magnetic flux emanating from thenear magnetic field source; and means for adjusting the first signalusing the second and third signals thereby compensating for the effectsof the near magnetic field source.
 25. The torque sensor of claim 24,wherein the at least one region is magnetized so that all of the domainmagnetizations in the region lie within at most a plus or minus 45degree limit of a circumferential direction of the member.
 26. Thetorque sensor of claim 24, wherein the magnetic field sensors are vectorsensors.
 27. The torque sensor of claim 26, wherein the vector sensorsare one of a Hall effect, magnetoresistance, magnetotransistor,magnetodiode, MAGFET field sensors, or fluxgate magnetometer.
 28. Thetorque sensor of claim 24, wherein the member is a shaft incorporated inan on-road or off-road vehicle, a ship, or an industrial process. 29.The torque sensor of claim 24, wherein the pre-determined first andsecond distances are substantially the same.
 30. The torque sensor ofclaim 24, wherein the pre-determined first and second distances are suchthat an average of the second and third signals approximates the valueof the ambient magnetic flux present at the location of the at least oneprimary magnetic field sensor.
 31. The torque sensor of claim 24,wherein the torque sensor comprises two primary magnetic field sensors;one secondary magnetic field sensor axially spaced in the firstdirection; and one secondary magnetic field sensor axially spaced in thesecond, opposite direction.
 32. The torque sensor of claim 31, whereinone of the primary magnetic field sensors and one of the secondarymagnetic field sensors are arranged on one side of the member, andwherein the other of the primary magnetic field sensors and the other ofthe secondary magnetic field sensors are arranged on an opposite side ofthe member.
 33. The torque sensor of claim 31, wherein all four of thefield sensors are arranged substantially on one side of the member andapproximately opposite the near magnetic field source on the oppositeside of the member.
 34. The torque sensor of claim 24, wherein thetorque sensor comprises four primary magnetic field sensors; twosecondary magnetic field sensors axially spaced in the first direction;and two secondary magnetic field sensors axially spaced in the second,opposite direction.
 35. The torque sensor of claim 24, wherein theactive region comprises two axially-spaced regions, the first beingmagnetized in a first substantially circumferential direction and theother being magnetized in a second substantially circumferentialdirection opposite the first direction in such a manner that the torqueapplied to the member is proportionally transmitted to the activeregion, wherein the at least one secondary magnetic field sensor axiallyspaced in the first direction is proximate one of the regions, andwherein the at least one secondary magnetic field sensor axially spacedin the second, opposite direction is proximate the other region.
 36. Thetorque sensor of claim 35, wherein the torque sensor comprises twoprimary magnetic field sensors; one secondary magnetic field sensoraxially spaced in the first direction; and one secondary magnetic fieldsensor axially spaced in the second, opposite direction.
 37. The torquesensor of claim 36, wherein one of the primary magnetic field sensorsand one of the secondary magnetic field sensors are arranged on one sideof the member, and wherein the other of the primary magnetic fieldsensors and the other of the secondary magnetic field sensors arearranged on an opposite side of the member.
 38. The torque sensor ofclaim 35, wherein the torque sensor comprises four primary magneticfield sensors; two secondary magnetic field sensors axially spaced inthe first direction; and two secondary magnetic field sensors axiallyspaced in the second, opposite direction.
 39. The torque sensor of claim24, wherein the primary and secondary magnetic field sensors areoriented substantially normally to the surface of the member.
 40. Thetorque sensor of claim 24, wherein the active region comprises threeaxially-spaced regions, the middle region being magnetized in a firstsubstantially circumferential direction and the outer regions beingmagnetized in a second substantially circumferential direction oppositethe first direction in such a manner that the torque applied to themember is proportionally transmitted to the active region, wherein theat least one secondary magnetic field sensor axially spaced in the firstdirection is proximate one of the outer regions, wherein the at leastone secondary magnetic field sensor axially spaced in the second,opposite direction is proximate the other outer region.
 41. The torquesensor of claim 40, wherein the torque sensor comprises two primarymagnetic field sensors; one secondary magnetic field sensor axiallyspaced in the first direction; and one secondary magnetic field sensoraxially spaced in the second, opposite direction.
 42. The torque sensorof claim 41, wherein one of the primary magnetic field sensors and oneof the secondary magnetic field sensors are arranged on one side of themember, and wherein the other of the primary magnetic field sensors andthe other of the secondary magnetic field sensors are arranged on anopposite side of the member.
 43. The torque sensor of claim 40, whereinthe torque sensor comprises four primary magnetic field sensors; twosecondary magnetic field sensor axially spaced in the first direction;and two secondary magnetic field sensors axially spaced in the second,opposite direction.
 44. The torque sensor of claim 41, wherein all fourof the field sensors are substantially on one side of the member andapproximately opposite the near field source on the opposite side of themember.
 45. The torque sensor of claim 40, wherein the primary andsecondary magnetic field sensors are oriented substantially normally tothe surface of the member.
 46. The torque sensor of claim 45, whereinthe primary and secondary magnetic field sensors are orientedsubstantially normally to the surface of the member at the respectiveboundaries between the regions.